Smelting furnace

ABSTRACT

A smelting furnace having a vessel ( 102 ) for receiving material to be smelted. An inner surface ( 109 ) of the furnace is concave and reflective, at least an upper part thereof. A conductive electrode ( 120 ) of the furnace is continuously formed in the furnace by casting.

This invention relates to a smelting furnace.

In one aspect, the invention provides a smelting furnace, a vessel of the furnace for receiving material to be smelted having an inner surface which at least at an upper portion thereof is concave and reflective.

The furnace may have an electrode at least a portion of which is within the interior of the vessel, for heating said material by application of electric potential to the electrode.

Means may be provided for introducing inert gas into the interior of the vessel, for ionisation under influence of said electric potential, to cause the gas to form a heated plasma, for effecting said heating of the material to be smelted.

The invention also provides a smelting furnace having electrode forming means for forming a conductive electrode, for use in heating material in the furnace by passage of electric current applied via the electrode, said electrode forming means being adapted to receive fluid material for forming the electrode such that the material sets in the interior of the furnace to form the electrode, such the electrode is positioned in the furnace for application of said electric current.

The means for forming a conductive electrode may include means for deriving off-gas from the interior of the furnace during said smelting, means for deriving from the off-gas carbonaceous ash material, means for combining said ash material with a liquid carbonaceous material to from said fluid material, and means for introducing said fluid material into said electrode forming means.

The electrode forming means may be in the form of an annular structure, whereby in use to cause said electrode to be formed from said fluid material in a downwardly depending annular form.

Means may be provided for introducing inert gas into said furnace through said electrode.

The furnace may be arranged for transforming said fluid material to solid form, for forming the electrode, under action of heat in the furnace.

The invention further provides a method of smelting material by electrical heating using an electrode in a furnace, wherein the electrode is formed by casting it in the furnace.

Carbonaceous ash material derived from the off-gas may be combined with a liquid carbonaceous material to form a fluid material, the fluid material being introduced into electrode forming means, to form the electrode.

By this method, the electrode may be formed as a downwardly depending annular member. The liquid carbonaceous material may be pitch.

The extruded annular member may be set by heat in the furnace.

The invention is further described by way of example only with reference to the accompanying drawing in which:

FIG. 1 is a diagrammatic representation of a smelting furnace formed in accordance with the invention, together with ancillary equipment;

FIG. 2 is a vertical cross-section of the smelting furnace of FIG. 1;

FIG. 3 is an enlarged cross-section on the line 3-3 in FIG. 2;

FIG. 4 is an enlarged vertical section of the region “A” in FIG. 1;

FIG. 5 is an enlarged vertical section of the region “B” in FIG. 1; and

FIG. 6 is a flow diagram of illustrating processing steps for continuous formation of a smelting furnace electrode in accordance with the invention.

The furnace 100 illustrated in FIGS. 1 and 2 has a smelting vessel 102 defining therewithin an internal chamber 104. The vessel is formed predominantly of metal, having inner and outer walls 106, 108 with a space 110 therebetween. One or more ducts 112 are provided to enable a suitable coolant liquid such as sodium to be passed into the space 110 for circulation therewithin, for cooling the vessel 102 in use thereof.

The lower part 114 of the vessel 102 is of dished form adapted to receive material 116 which is to be smelted. The upper part 118 of the vessel 102 is of concave domed configuration, for example, of substantially hemispherical or paraboloid configuration. To facilitate assembly and disassembly of the vessel such as in manufacture or for maintenance, the upper and lower parts 114, 118 may be separately formed and attached together by releasable means (not shown).

Broadly, material 116 to be smelted is positioned in the vessel 102 so to lie on the lower part 114 of the vessel 102. Smelting is effected by application of an electric potential between a central downwardly depending carbonaceous electrode 120 in the vessel 102, which terminates above the upper surface 117 of the material 116, and a central electrode 137 in the base of the vessel 102. The electrodes 120, 137 are electrically insulated from the vessel 102. During smelting, gas (which may be an inert gas such as argon) is introduced into the chamber 104, immediately above surface 117 via an upright duct 145 which extends vertically within a central lengthwise extending passageway 122 in the electrode 120. The passage of the electric current causes ionisation of the gas introduced into the chamber 104, to cause the gas to form a heated plasma for heating and smelting of material 116. The electric supply may be a conventional low voltage high current DC source 119 which applies potential to the electrodes such that the electrode 120 is the cathode and the electrode 137 is the anode.

The electrode 120, which in use of the furnace 100, is consumed by erosion of the lower end thereof, is formed in the vessel 102 by a continuous casting process, so that it is continuously replenished. Particularly, the furnace has an electrode forming means 70 arranged such that the electrode 120 is continuously formed in a vertically elongate space 141 of annular cross section, defined between inner and outer coaxial hollow cylindrical members 123, 125 of the electrode form means 70. The electrode 120 is correspondingly formed so as to be of annular cross-section, to define therewithin the central passageway 122.

Cylindrical member 125 extends axially of the vessel 102, from an upper end which is exteriorly positioned above the upper part 118 of the vessel, downwardly through a central opening 127 in the vessel 102, above the upper part 118, and into the chamber 104. The member 125 terminates at a lower end positioned so as to be, in use of the furnace 100, a short distance above the surface 117 of the material to be smelted. The member 125 is electrically insulated from the vessel 102 by an annular insulation element 138 surrounding the periphery of the member 125 towards its upper end and positioned in opening 127. The cathode 120 is electrically insulated from the vessel 102 by an annular insulation ring 139 positioned in a lower central opening 135 in the vessel 102 and surrounding the periphery of anode 137.

The upper end of cylindrical member 125 is closed by an upper transverse wall 143. The lower end of the cylindrical member 125 is open. The upper end of duct 123 extends through a central opening in transverse wall 143 to an upper end then leads, through a control valve 148, to a receptacle 170 for material to be smelted, in flowable, eg granular form. By operation of the valve 148, the material in receptacle 170 can be released from the receptacle to pass down the interior of the cylindrical member 123 to be deposited in the chamber 104.

The duct 145 extends coaxially within the cylindrical member 123. It opens at its lower end at a location within the member 123, and at a relatively short distance above the bottom of chamber 104. The upper end passes sealingly though an opening in member 123, and leads to a source of inert gas (not shown). In use, the gas is introduced into the duct 145 from the source to flow down the duct 145, and exit from an open lower end of the duct a short distance above the lower end of electrode 120.

The lower, open, end of member 123 is open, and is located at about the same vertical height as the lower end of cylindrical member 125.

A duct 147 extends sidewardly from cylindrical member 125, at the upper end thereof, and provides communication between the space 141 between the members 123, 125, at the upper end thereof. Duct 147 communicates with the lower part of a hopper 152 which receives a particulate material 157 formed mainly from carbon ash. By operation of a valve 149 in duct 147, the material 157 in hopper 152 is controllably released from the hopper 152, to flow through duct 147 into the space 141 at the top thereof.

A ring-like feed member 161 is provided, surrounding the cylindrical member 125 at the upper end thereof, above vessel 102, but below the duct 147, and sealingly attached, at the inner periphery thereof to the external cylindrical surface of the member 125. As best shown in FIG. 3, feed member 161 has an array of equi-angularly disposed radial passageways 165 which at outer ends communicate with externally extending ducts 163.

At inner ends, the passageways 165 communicate with the space 141 via respective side openings 171 in the member 125.

The passageways 165 are normally closed by ball valves 173 having balls 175 urged by springs 179 into contact with annular valve seats 177 formed in passageways 165.

Referring now to FIG. 5, the ducts 163 communicate with a distribution element 185 of a delivery device 181, which is coupled to a receptacle 187 for liquid pitch 191. The delivery device 181 has a hollow cylinder 193 closed at one end by the distribution element 185. The ducts 163 terminate at openings 201 in the distribution device 185 and which provide communication between the ducts 163 and the interior of cylinder 193.

The receptacle 187 has a lower outlet which communicates via a duct 195 with a side opening 205 in the cylinder 193.

A piston 197 is slidingly and sealingly retained in cylinder 193, for reciprocating movement therewithin. Piston 197 is pivotally connected to one end of a connecting rod 199, the other end of which is pivotally connected at an eccentric location to a drive disc 203, mounted to the output shaft of a motor 206. When motor 206 is operated, disc 203 is rotated to cause piston 197 to be reciprocated in cylinder 193, by action of connecting rod 199. The side opening 205 in cylinder 193 is so positioned that, as the piston is reciprocated in cylinder 193 pursuant to operation of motor 206, successive charges of pitch 191 from the receptacle 187 are delivered to the cylinder 193, as the piston 197 is withdrawn in the cylinder to the location shown in FIG. 5, and then forced by subsequent advancement of the piston in the cylinder through openings 201 and through the ducts 163. The pressure applied by the piston 197 to each charge of pitch so forced into the ducts 163 is such that the pressurised pitch acts to open the ball valves 173. Particularly, pressure so exerted against balls 175 moves them away form the valve seats 177 against the bias provided by springs 179. By this, pitch 191 is transported from receptacle 187 through ducts 163 to pass via balls valves 173, ducts 163, passageways 165 and openings 171 into the upper part of space 141.

The pitch 191 introduced into the upper part of space 141 is introduced around the periphery of the particulate material 157 introduced into the space 141 via duct 147, and becomes intermingled with that material to form a body of carbonaceous material which, under continued operation of the furnace, descends in the space 141. As it descends, the material is baked by heat from the operation of the furnace to form the electrode 120.

As mentioned, the electrode 120 is continuously consumed in operation of the furnace. However because the electrode 120 is, as above described, formed by a continuous casting process, it is possible, by matching the rate of formation of the electrode 120 with the rate of erosion thereof to ensure that the electrode 120 is maintained at a stable length, and so that the lower end of the electrode 120 is maintained at a stable height above surface 117. This can be effected by appropriate control of the speed of rotation of motor 206, to control the rate of feed of the pitch 191, and by regulation of the inflow rate of the particulate material 157, by control of the valve 149 in the duct 147.

The electric potential applied between cathode 120 and anode 137 is sufficient to enable ionisation of the gas passed into the chamber 104 through duct 145 so as to form a heated plasma in the chamber 104 which melts the material 116. The interior surface 109 of the inner wall 106, at least at the upper part of the vessel 102, is rendered to a highly reflective state, such as to exhibit a mirror finish. In consequence, and because of the concave shape of the upper part of surface 109, heat is reflected within the chamber 104, so that a relatively lesser portion thereof is lost from the vessel 102 and efficient heating and smelting of the material 116 results. Molten metal from material 116, derived by the smelting, may be withdrawn via a side passageway 130 which passes through side walls 106, 108. Slag 254, resulting from the smelting may be withdrawn via a passageway 131 which passes through side walls 106, 108, entering chamber 104 at a height somewhat above the location where passageway 130 communicates with the chamber 104. In case of smelting some materials 116, it may be desirable to recover heavier metals 256, which collect at the lower part of the chamber 104 during smelting. As shown, the walls 106, 108 are configured, at the bottom of the vessel 102, to form a small recess 225 around the location of the cathode 120 at which the heavier metals 256 accumulate. There is an outlet duct 133 leading from the lower part of the surface of recess 225, through which molten metals so recovered by smelting may be taken from chamber 104.

The cathode 120 is preferably formed with upstanding fingers 137A which are electrically insulated from each other by suitable surrounding insulating material.

Walls of pipes defining the passageways 130, 133 and 131 are provided with heating coils wound therearound, at locations adjacent the interior of the chamber 102, such as between walls 106, 108, as shown. Electric current is passed through these to inhibit solidification of molten materials therewithin.

Off gas generated during smelting is taken from chamber 104 via an upper outlet duct 132.

As mentioned, at least the upper part of the surface 109 of the interior of the vessel 102 (i.e. that formed by inner surface of the upper part of the wall 106) is rendered to a highly reflective state such as by polishing it, preferably to a mirror finish. It has been found that, by this, the heating effect within the vessel 102 is greatly enhanced and efficient smelting can be achieved.

When smelting certain metals such as magnesium, the metal tends to come off as a vapour in chamber 104, which needs to be condensed to recover the metal in liquid form. In a refractory-lined kiln, the vapour tends to adhere to the refractory and recovery is impeded. In the furnace 100, however, recovery may be effected by use of a simple splash condenser at a suitable outlet. FIG. 4 shows such an arrangement. In this, the duct 132 is defined by a pipe 238 leading from the chamber 104, and which communicates with a splash condenser 258, via an expansion chamber 260. An electrically conductive coil 244 is provided around the pipe 238, between vessel 102 and expansion chamber 260, and electric current is passed this to heat this part of the pipe to inhibit condensation of vapour therein. Vapour admitted to chamber 260 is cooled by expansion in chamber 260 and the expanded, and somewhat cooled. The vapour is then conveyed to the splash condenser 258, at which it is condensed. The part of pipe between expansion chamber 260 and splash condenser 258 is cooled by passing suitable cooling fluid through a helical cooling element positioned around that part of the pipe.

The smelter may be used for a smelting variety of materials such as ilmenite for recovery of titanium.

The material 157 may comprise carbon ash which has been subjected to chemical action, together with graphite powder, in a mechano fuser. The resultant material may comprise small particles of carbon ash surrounded by graphite powder. The carbon ash may be recovered from the furnace 100, particularly from the off gas at opening 132 by a process illustrated in FIG. 6.

As shown in FIG. 6, the off gas 140 passes to a precipitator 142. Fine metal dust, carbon and ash 180 recovered from the precipitator is passed to a magnetic separator 182 which may be of the electrostatic type. Separated metals 200 from the separator 182 are returned to the furnace and separated carbon ash 190 is then passed to a mechano fuser 192, together with graphite powder 202 to form the material 157 which is directed to the space 141 as described. Material separated from the fine metal dust, carbon and ash in the precipitator 142 is passed to a vortex scrubber 505, which also receives micronised limestone 511. From the vortex scrubber 505, there emerges clean air 507 and separated limestone slurry 509. Slurry 509 has entrapped materials such as sulphur and superfine gases or dust. The slurry may be disposed of as required.

Particular exemplary applications of the invention are:

A) Smelting and recovery of metal from waste materials recovered from electric arc furnaces when processing metal (arc furnace dust).

-   -   Typically, substantial quantities of dust-like material are         produced in such processing. The material may include         carbonaceous dust from the carbon electrodes of the furnace. It         typically also includes particles derived the material being         processed, eg metal, and from flux employed in processing. These         particles may include metal oxides, calcium etc. The dust like         materials are typically recovered by extraction of gas and dust         from the electric arc furnace interior, and passing that         material to a suitable dust collector (eg a “bag-house). The         materials are troublesome, in that they are difficult to         contain, and in typical smelting operations need to be stored         rather than being used in some subsequent industrial process.         These materials can however be used as raw material in a         smelting furnace formed in accordance with the invention. That         is, the material can be passed via a suitable transport system         (such as a supply duct) to the interior of the furnace for         smelting to recover the metal contained in the material.         B) Recovery of metal from slag produced by, eg electric arc         furnaces or blast furnaces.     -   Slag produced when smelting metal ores typically includes metal         or metal ore from the material to be smelted, as well as         material derived from the flux employed in smelting, eg         limestone, silica etc. Presently, the slag is of little         commercial worth. However, using the techniques of the present         invention, it is possible to smelt the slag to recover metal         from it. Thus slag derived from an electric arc furnace during         smelting metal ores such as ores containing iron, zinc and/or         lead may be reduced to particulate form and used as feed for a         furnace constructed in accordance with this invention, in order         to smelt the slag and recover the metal from it.         C) Smelting of metal ores     -   Metal ores subjected to concentration by conventional techniques         and crushed to particulate form may be used as feed for a         furnace constructed in accordance with this invention, in order         to smelt the ore and recover the metal from it.

It will be apparent to the skilled addressee that many modifications and changes may be made to the invention without departing from the spirit and scope thereof.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

LIST OF PARTS

-   Electrode Forming Means 70 -   Furnace 100 -   Smelting Vessel 102 -   Internal Chamber 104 -   Inner Wall 106 -   Outer Wall 108 -   Upper Part of the Surface 109 of the Interior of the Vessel 102 -   Space 110 -   Duct 112 -   Lower Part 114 of Vessel 102 -   Material 116 -   Upper Surface 117 of Material 116 -   Upper Part 118 of Vessel 102 -   DC Current Source 119 -   Carbonaceous Electrode (Cathode) 120 -   Central Lengthwise Extending Passageway 122 -   Inner Hollow Coaxial Hollow Cylindrical Member 123 -   Outer Hollow Coaxial Hollow Cylindrical Member 125 -   Central Opening 127 -   Side Passageway 130 -   Passageway 131 -   Duct Outlet 132 -   Outlet Duct 133 -   Lower Central Opening 135 -   Central Electrode (Anode) 137 -   Fingers 137A -   Annular Insulation Ring 139 -   Off Gas 140 -   Space 141 -   Precipitator 142 -   Upper Traverse Wall 143 -   Upright Duct 145 -   Sidewardly Extending Duct 147 -   Control Valve 148 -   Valve 149 -   Hopper 152 -   Particulate Material 157 -   Ring Like Feed Member 161 -   Duct 163 -   Equi-angularly disposed radial passageway 165 -   Receptacle 170 -   Opening 171 -   Ball Valve 173 -   Ball 175 -   Annular Seat 177 -   Spring 179 -   Fine Metal Dust, Carbon and Ash 180 -   Delivery Device 181 -   Magnetic Separator 182 -   Distribution Element 185 -   Receptacle 187 -   Separated Carbon Ash 190 -   Liquid Pitch 191 -   Mechano Fuser 192 -   Hollow Cylinder 193 -   Duct 195 -   Piston 197 -   Rod 199 -   Separated Metals 200 -   Opening 201 -   Graphite Powder 202 -   Drive Disk 203 -   Opening 205 -   Motor 206 -   Opening 225 -   Pipe 238 -   Coil 244 -   Slag 254 -   Heavier Materials 256 -   Splash Condenser 258 -   Expansion Chamber 260 -   Vortex Scrubber 505 -   Clean Air 507 -   Limestone Slurry 509 -   Micronised Limestone 511 

1. A smelting furnace, a vessel of the furnace for receiving material to be smelted having an inner surface which at least at an upper portion thereof is concave and reflective.
 2. A smelting furnace as claimed in claim 1, having an electrode at least a portion of which is within the interior of the vessel, for heating said material by application of electric potential to the electrode.
 3. A smelting furnace as claimed in claim 2 having means for introducing inert gas into the interior of the vessel, for ionisation under influence of said electric potential, to cause the gas to form a heated plasma, for effecting said heating of the material to be smelted.
 4. A smelting furnace having electrode forming means for forming a conductive electrode, for use in heating material in the furnace by passage of electric current applied via the electrode, said electrode forming means being adapted to receive fluid material for forming the electrode such that the material sets in the interior of the furnace to form the electrode, such the electrode is positioned in the furnace for application of said electric current.
 5. A smelting furnace as claimed in claim 4 including means for deriving off-gas from the interior of the furnace during said smelting, means for deriving from the off-gas carbonaceous ash material, means for combining said ash material with a liquid carbonaceous material to from said fluid material, and means for introducing said fluid material into said electrode forming means.
 6. A smelting furnace as claimed in claim 5 wherein said electrode forming means is in the form of an annular structure, whereby in use to cause said electrode to be formed from said fluid material in a downwardly depending annular form.
 7. A smelting furnace as claimed in claim 6 including means for introducing inert gas into said furnace through said electrode.
 8. A smelting furnace as claimed in claim 6 or claim 7 arranged for transforming said fluid material to solid form, for forming the electrode, under action of heat in the furnace.
 9. A method of smelting material by electrical heating using an electrode in a furnace, wherein the electrode is formed by casting it in the furnace.
 10. A method as claimed in claim 9, including deriving carbonaceous ash material from the off-gas, combining said ash material with a liquid carbonaceous material to form a fluid material, and introducing said fluid material into electrode forming means, to form the electrode.
 11. A method as claimed in claim 10 wherein said electrode is formed as a downwardly depending annular member.
 12. A method as claimed in claim 10 or claim 11 wherein said liquid carbonaceous material is pitch.
 13. A method as claimed in any one of claims 10 to 12 wherein the fluid material is set by heat in the furnace to form the electrode. 